1. Field of the Invention
This invention relates to the field of chemical analysis and, more specifically, to the interaction of electromagnetic radiation with a sample to determine certain intrinsic characteristics such as the rate at which a chemical reaction may be progressing, and by extension the concentration of one or more specific components in the sample.
This invention pertains even more particularly to a chemical analyzer which employs a contactless methodology, based on the transmission of electromagnetic radiation in the radio frequency ("RF") range along a known path through a volume element of a sample.
This invention also relates to various probe and system designs which facilitate the use of RF radiation attenuation as the basis for the measurement of certain chemical characteristics of a sample.
2. Background Art
One ordinarily skilled in chemical analysis is generally familiar with a variety of apparatus which measure changes in the way a sample interacts with an electromagnetic field to obtain a measure of the concentration or change in concentration of components in the sample.
One example of such a device is the conductivity meter. As the name implies, these devices measure the electrical conductivity of the sample. Most of these devices have electrode probes which must be placed in contact with the sample. This is known to create several disadvantages, including sample contamination, probe contamination, and probe degradation. Several other classes of devices avoid the necessity of placing a probe in contact with the sample. These include spectrophotometers and high frequency titrators.
Spectrophotometers measure changes in a light signal as it is propagated through a sample. This makes them suitable for chemical analysis of compounds which interact with radiation of the infrared, visible, and ultraviolet frequencies. Compounds which do not interact with these frequency ranges, however, are not susceptible to measurement by such devices.
High frequency titrators represent the first attempts at measuring changes in sample interactions with RF fields. They measure resistance, capacitance, or inductance of a tuned circuit incorporating the sample. As a result they are, as a class, susceptible to changes in complex impedances and exhibit nonlinear response and calibration problems.